1. Field of the Invention
This invention relates to the field of changing displays, in particular lenticular signs having a plurality of lenses aligned to at least two distinct interleaved and segmented background fields, whereby the lenses display only one field and then only the other field as the perspective of the viewer changes, e.g., while passing the sign. The sign can display related copy on the two fields, can simulate motion via animation, etc. According to the invention the lenses are parts of a lens panel made from discrete segments of one or more lens elements. The lens elements are mounted to overcome variations in dimensions of individual lenses, to facilitate access for changing the copy, and include a framing structure fixing the lenses relative to the image. In a large format sign the invention overcomes problems with misalignment of the lens elements and the background field segments which would detract from the discrete selection of one or the other of the images for viewing.
2. Prior Art
Lenticular signs having two or more interleaved display fields, and a superimposed lens arrangement to shift between them, are well known in small displays such as toys but have not been successfully applied to large format advertising displays, especially with changeable (reloadable) copy, due to very substantial problems in achieving the necessary accuracy in large signs. The basic idea of a lenticular sign is to provide a regular pattern of individual lenses across a field, positioned over a background panel on which the copy appears. The copy includes two or more images, each of which has been subdivided, e.g., in strips for strip-like lenses or in other shapes corresponding to the lens shapes. These strips or the like from the two or more images are interleaved on the background panel such that a segment from a corresponding area of each of the two patterns is placed behind each lens segment. Due to diffraction through the lenses, the light path along the direction of view for most viewing angles exposes one of the image segments only (for viewer perspectives or angles which are normal to the lens and aligned to the image segments, both images appear). By varying the angle of view and/or the relative alignment of the lenses to the image panel, the display is caused to select one or another pattern for viewing. This phenomena can be applied to a fixed arrangement of the lens panel relative to the image panel, whereupon the angle of view changes as the viewer passes in front of the sign, or alternatively the lens panel and image panel can be relatively moved in an oscillating motion by a motor or the like, to cause the image presented to a stationary viewer to cycle between the respective images.
Lenticular signs can have lens elements disposed in an X-Y array or in a strip-like array. Examples of such signs in an X-Y array include U.S. Pat. Nos. 2,371,172, 2,507,975-Hotchner; and U.S. Pat. No. 2,833,176-Ossoinak. Examples of similar arrangements for multiple image displays in a strip like format are disclosed for example in U.S. Pat. No. 3,314,179-Leach; U.S. Pat. No. 3,918,185-Hasala and U.S. Pat. No. 4,255,380-Bjorkland.
In each case, the objective is to place the lens elements at a distance from an image panel determined by the shape or focal length of the lens segments. The image panel has two or more segmentally interleaved images with segments of each of the two or more images positioned behind the lens elements. The image segments are placed side by side behind the lenses to define an image segment group. Each lens displays the underlying discrete segment of each of the images from its group, one at a time. As the viewer's perspective on the lens elements changes relative to the image segments, the lens elements all display their individual image segments from the same one of the interleaved fields, thereby changing from a display of one overall image field to a display of another.
Segmented lenticular signs of the foregoing description are well known in connection with toys and similar small, hand held display panels. In small display panels, the lens segments are formed integrally, e.g., as a molded sheet with ridges on one side, permanently attached to the image panel such that the alignment of the lenses to the image segments is relatively assured. Typically, the image is printed or glued onto the lens panel, which is molded of plastic to provide ridges forming the lenses. In connection with larger displays there are substantial problems incurred in applying the idea to a practical embodiment. A major difficulty in setting up a large display of this type is that the pitch of the lens elements and the position of the lens elements must correspond very precisely with the segments of the display fields and it is not readily possible or practical to provide an integral lens panel and image in a large sign. Each lens across the display must be positioned to correspond to the respective division between the display field segments to which that lens segment is applied. In order to achieve the necessary accuracy substantial attention must be paid to the dimensions and relative positions of the lenses, the dimensions and relative positions of the display field segments, and the correct placement of the lenses relative to the display field segments.
It would be quite desirable to provide a large format lenticular sign as a form of advertising. The changeable nature of the copy and the possibility of an animated presentation would generate substantial interest. A given space can display two messages rather than one. Preferably such a sign would allow the copy to be changed periodically in a convenient manner, as typical of billboards.
However, a large format sign is more difficult to arrange accurately than a small format sign, due to dimensional tolerances in manufacturing and due to problems in alignment upon mounting the lenses relative to the interleaved image segments. For example, in a hot forming molding or extruding process for plastics, the resulting dimensions may be determined in part by the temperature of processing and the cooling cycle. Where a lens panel is made in this manner the edges of the panel will normally cool more quickly than the central area, resulting in variations in pitch of the lenses across the lens panel due to differential shrinkage. While a mold or extruder having a pitch which varies to cancel the effects of differential shrinkage is theoretically possible, the process and resulting product would be too expensive to be cost effective.
Differential thermal expansion can also occur in use, between a lens element and an image panel particularly where the lens element forms the external panel over an image panel, thereby forming a greenhouse-like heat trap. These problems are aggravated if one attempts to provide a large format display wherein the image panel is to be changeable to allow a change in copy while retaining the lenses and the image panel mounting structure. The same features which allow access to the image panel for changing it tend to allow misalignment, pitch variation, or improper spacing of the lenses relative to the image panel segments.
Variations in pitch substantially detract from the effectiveness of the multiple field display. Where the pitch is inaccurate a viewer of the display will see portions of both displays or different ones of the display fields in different areas of the display. Thus the images are superimposed or mixed, rather than, as intended, changing crisply from a display of only one entire display field followed by the other entire display field. These problems, and the substantial attention to dimensions and alignment which are required to overcome them, have made large format lenticular signs impractical. While smaller signs have been produced (e.g., up to one or two feet on a side), the technology has not allowed a larger sign as suitable for advertising, e.g., occupying all or a substantial part of a billboard, which may be 10 meters on a side. It has been too difficult or expensive to provide the necessary precision in the dimensions and arrangement of the lens panel and the display panel, particularly since no means were provided to allow the display panel to be changed while re-using the lens panel.
According to the present invention, however, the dimensional tolerance of a lens panel is improved by dividing the lens panel into discrete lens elements of one or more lenses, which are arranged to resiliently bear against one another. Whereas the tolerances of individual lens elements may vary, the pitch proceeding across the overall display remains very regular. In a preferred embodiment wherein two or more lenses form a lens element, dimensional variation of the lenses can be corrected when attaching them to form a lens element, whereby a large sign produced from a series of abutted lens elements has a very regular pitch, much better than possible considering the dimensional tolerances of the lenses themselves. The individual mounting of the lens segments also permits the entire display to be assembled and disassembled readily for cleaning, replacement or for changing the sign copy. The pitch of the lenses and the display panel can be relatively varied across the face of the sign. For example, by increasing the pitch of the display field segments relative to the pitch of the lenses, the lens segments select the display fields accurately at a closer perspective where parallax would otherwise interfere. The invention thus provides a practical and effective application of the field of lenticular signs to large format sign for example, as appropriate for advertising billboards.